Code 33, 34 - poss ECM Question
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From: Rindge NH
Code 33, 34 - poss ECM Question
Background:
I have the FSM and followed the flow chart, repeated several times to verify my results. I also did numerous forum and google searches, even printed out Agent 86's links on the subject. Swapped out both relays.
Answered 'YES' at each step 1-5 in the 'CODE 33' chart, including answering 'OK' at step 5, voltage between 4-6 at pin C, which leads to either loose terminals, or faulty MAF.
I then tried the flow chart for 'CODE 34'. Answered 'NO' at step 2 which involved clearing the codes, disconnect the MAF, start engine and run it above 2300 for 1 minute, or until a code is set.
I never got a code, and the car ran extremely rough and smelled of fuel. Answer 'NO' leads to a faulty ECM. Should the car run rough with the MAF disconnected, or enter a limp home mode and run relatively smoothly?
I'm not willing to throw parts at it, so I thought I'd probe some more. I repeated the test for code 33 to the point that verifies voltage between 4 and 6 at the ECM connector pin c - signal voltage. Got a reading of 4.99V. ECM supplies 5v, correct?
Inserted the Eckler's MAF test tool in line between the MAF and connector at the harness (car wiring is now connected to the MAF through the test tool, which plugs into the MAF). Hooked up a DVM to signal pin C, measured around 2.5V with the engine off. I remember seeing that GM MAF's should be around 2.5V at idle and increase voltage as the throttle opens?
Started the car and voltage at pin C dropped to 0.05V and stayed there. It never varied with throttle position. Shut the car off, voltage comes back up to 2.5 for 30 seconds or so then drops to zero.
Next, I hooked up my DVM to the burn off pin d to look for burn off voltage. No voltage at start up (no voltage within 25 sec of fuel pump running, per FSM), looking good. At start up, 0.08V. No voltage spike after shutdown to indicate a burn off event. DVM went to zero around the same amount of time after shutdown as the signal voltage did.
What triggers the relays to supply burn off voltage?
The part that keeping me from running out and getting a MAF is the loss of signal voltage when the car is started coupled with the absence of burn off voltage and the result of 'CODE 4' testing. Or, could the MAF be that bad?
Any thoughts?
I have the FSM and followed the flow chart, repeated several times to verify my results. I also did numerous forum and google searches, even printed out Agent 86's links on the subject. Swapped out both relays.
Answered 'YES' at each step 1-5 in the 'CODE 33' chart, including answering 'OK' at step 5, voltage between 4-6 at pin C, which leads to either loose terminals, or faulty MAF.
I then tried the flow chart for 'CODE 34'. Answered 'NO' at step 2 which involved clearing the codes, disconnect the MAF, start engine and run it above 2300 for 1 minute, or until a code is set.
I never got a code, and the car ran extremely rough and smelled of fuel. Answer 'NO' leads to a faulty ECM. Should the car run rough with the MAF disconnected, or enter a limp home mode and run relatively smoothly?
I'm not willing to throw parts at it, so I thought I'd probe some more. I repeated the test for code 33 to the point that verifies voltage between 4 and 6 at the ECM connector pin c - signal voltage. Got a reading of 4.99V. ECM supplies 5v, correct?
Inserted the Eckler's MAF test tool in line between the MAF and connector at the harness (car wiring is now connected to the MAF through the test tool, which plugs into the MAF). Hooked up a DVM to signal pin C, measured around 2.5V with the engine off. I remember seeing that GM MAF's should be around 2.5V at idle and increase voltage as the throttle opens?
Started the car and voltage at pin C dropped to 0.05V and stayed there. It never varied with throttle position. Shut the car off, voltage comes back up to 2.5 for 30 seconds or so then drops to zero.
Next, I hooked up my DVM to the burn off pin d to look for burn off voltage. No voltage at start up (no voltage within 25 sec of fuel pump running, per FSM), looking good. At start up, 0.08V. No voltage spike after shutdown to indicate a burn off event. DVM went to zero around the same amount of time after shutdown as the signal voltage did.
What triggers the relays to supply burn off voltage?
The part that keeping me from running out and getting a MAF is the loss of signal voltage when the car is started coupled with the absence of burn off voltage and the result of 'CODE 4' testing. Or, could the MAF be that bad?
Any thoughts?
